Powder spraying is often used to apply a powder coating material to an article. Various spray technologies may be used including many electrostatic and non-electrostatic techniques. In most powder spraying operations, a significant amount of powder overspray is produced, meaning powder that is directed at the article but does not adhere to the article. Even with spray technologies that have a high transfer ratio, significant amounts of powder overspray may be produced.
The presence of powder overspray typically necessitates the use of a spray booth. A spray booth is used to contain or confine the powder overspray within a partially enclosed area. The spray booth may also be equipped with powder collection and recovery systems. Powder containment and collection are especially important for manual spraying operations wherein an operator is usually in relatively close proximity to the powder spray.
Spray booths can vary substantially in size depending on the articles being sprayed and the quantity of articles being sprayed. Some spray booths are conveyorized to permit automatic transfer of the articles into and through the booth.
A known spray booth design for containing and recovering powder uses cartridge filters and containment airflow. Such a system is sold by NORDSON(copyright) Corporation, Amherst, Ohio under the name ECONO-COAT(copyright) and VERSA-COAT(copyright) powder coating systems. The powder recovery system includes a series of vertically oriented cartridge style filters along one or more walls of the spray booth. A fan is used to create a substantial airflow within the booth. This airflow entrains the powder overspray. The fan draws the powder-laden air through the cartridge filters and exhausts the filtered air to the plant through a second set of filters called final filters. Powder collects on the cartridges, and the cartridges may be cleaned by applying a reverse pulse of air that knocks the powder off the cartridges to the collector base or booth floor. The motor fan, final filters and cartridge filters are assembled into a sealed housing to form a powder recovery module that can be mounted to a spray booth.
A significant limitation of such known systems, however, is that each powder recovery module is uniquely designed for a specific spray booth size. For example, for a given size booth, a fan and associated fan drive motor is used to produce an adequate air flow to contain the powder and draw the powder entrained air into the filters. The number and size of the cartridge filters are also determined by the size of the spray booth and required airflow to contain and recover the powder. Thus, for a given size spray booth, a powder recovery module is designed and fixed in terms of its air handling capacity. Although it is possible to add more modules for larger booths, this technique is not particularly efficient for smaller increases in spray booth size.
Another limitation of the known cartridge type recovery system is that to make a color change requires an extensive cleaning operation. While the filters are easy to replace, the associated housing and wrappers need to be cleaned prior to using a new powder color in the booth.
The need exists therefore for a more flexible and preferably modular cartridge-type powder recovery system that can have capacity added as the spray booth size increases. Such a design preferably will facilitate, if required, efficient color change operations.
In accordance with the invention, a powder recovery apparatus for a spray booth is provided that is modular in design to facilitate modifying the apparatus for increased or decreased air and filter capacity when the associated spray booth volume is changed. The modular design includes a base housing that encloses a motor driven fan wheel and one or more final or secondary filters. Vertically mounted on the base are one or more cartridge-style filters through which powder-laden air is drawn down into the base from the spray booth. In accordance with one aspect of the invention, the cartridges are partially surrounded by a wrapper that extends vertically to a height just above the cartridges. The wrapper is constructed such that additional wrappers may be vertically stacked to accommodate larger cartridges without having to modify the base. When the spray booth is increased in size, a larger motor and fan wheel or additional final filters may be installed when necessary in the same modular base.
In accordance with another aspect of the invention, the cartridge filters are arranged within a modular wrapper structure that is installed as a complete unit in a base. The modular cartridge assembly thus facilitates faster and easier color changes.
Still a farther aspect of the invention provides a fan cone in the base between the fan wheel and the air inlets to the base from the cartridges. The fan cone provides a transition air flow path such that the size of the fan wheel can be changed and easily interfaced to the air inlet without having to modify the base structure.
These and other aspects of the present invention will be fully explained and understood from the following detailed description of exemplary embodiments of the invention in view of the accompanying drawings.